Apple (AAPL) shares bucked the upward trend in tech stocks after Citigroup analysts cut iPhone sales estimates on Monday. The firm said share prices could see volatility in the near term as investors put an inordinate amount of focus on smartphone sales ahead of Apple's quarterly results at the end of October. The S&P 500 clinched its longest winning streak of 2015 as crude oil prices surged and boosted the energy sector. The benchmark index has gained more than 5 percent over the past five days. Twitter (TWTR) was among the best performers on markets after it named co-founder Jack Dorsey as its permanent CEO after months of speculation. Dorsey has been a frontrunner since serving as interim chief since July. TheStreet's Keris Lahiff has details from New York.